Fuel cell assembly comprising an improved catalytic burner

ABSTRACT

There is disclosed a fuel cell assembly comprising at least one horizontally arranged fuel cell stack that has numerous fuel cells, each comprising an anode, a cathode and an electrolyte situated between the anode and the cathode; combustible gas supply means for supplying combustible gas to the anodes of the fuel cells; anode gas withdrawal means for withdrawing the anode exhaust gas from the anodes; cathode gas supply means for supplying cathode gas to the cathodes of the fuel cells; cathode gas withdrawal means for withdrawing the cathode exhaust gas from the fuel cells; and recirculation means for recirculating at least one part of the anode exhaust gas and/or the cathode exhaust gas to cathodes of the fuel cells. The fuel cell assembly according to the invention is characterised in that the recirculation means comprise at least one catalytic burner with catalyst material for burning the remaining combustible gas contained in the anode exhaust gas, said burner being situated at the side of the fuel cell stack.

This application claims priority to German patent applications DE 102008 047 920.9 filed on Sep. 19, 2008 and DE 10 2009 013 598.7 filed onMar. 17, 2009 and PCT application PCT/EP2009/006701 filed on Sep. 16,2009, which are hereby incorporated by reference in their entireties.

In one embodiment of the present disclosure concerns a high temperaturefuel cell arrangement, especially a molten carbonate fuel cellarrangement, as well as a method for operation of such a fuel cellarrangement.

To generate electrical power by means of fuel cells a larger number offuel cells are ordinarily arranged in the form of a stack, each fuelcell having an anode, a cathode and an electrolyte arranged in between.The individual fuel cells are each separated by bipolar plates andelectrically contacted. Current collectors are provided on the anodesand cathodes, which serve for electrical contact of the anodes andcathodes, on the one hand, and to supply reaction gases to them, on theother. Sealing elements are provided in the edge area of the anode,cathode and electrolyte matrix, which form lateral sealing of the fuelcells and therefore the fuel cell stack from emergence of anode andcathode gas.

The electrolyte material in a molten carbonate fuel cell typicallyconsists of binary or ternary alkali carbonate melts (for example, mixedmelts of lithium and potassium carbonate), which are fixed in a porousmatrix. Molten carbonate fuel cells typically reach working temperaturesof about 650° C. during operation. A reaction of hydrogen with carbonateanions to water and carbon dioxide with release of electrons then occurson the anode side. Oxygen reacts with carbon dioxide to carbonate ionson the cathode side with absorption of electrons. Heat is then released.The alkali carbonate melts used as electrolyte, on the one hand, supplythe carbonate ions necessary for the anode half-reaction and, on theother hand absorb carbonate ions that form in the cathode half-reaction.A hydrocarbon-containing energy carrier, like methane, for example,which can come from natural gas or biogas, as well as water, aregenerally supplied in practice to the anode side of the fuel cell, fromwhich hydrogen required for the anode half-reaction is produced byinternal reforming. The anode waste gas is mixed with additionallysupplied air and then oxidized catalytically to eliminate any residualcomponents of the fuel gas. The formed gas mixture now contains carbondioxide and oxygen, i.e., precisely the gases required for the cathodehalf-reaction so that anode waste gas can be introduced directly to thecathode half-cell after fresh air supply and catalytic oxidation.

The hot exhaust emerging at the cathode output is pollutant-free and canbe further used for heat. The electrical efficiency of the moltencarbonate fuel cell is already 45 to 50% and when the heat released inthe overall process is used, an overall efficiency of about 90% can beachieved.

The applicant was able to integrate the fuel cell stack and all systemcomponents operating at high temperature in a common gas-tightprotective housing. The efficiency of the system is therefore improved,on the one hand, and an arrangement could be achieved, on the other, inwhich the cathode gas stream can circulate freely in the internal spaceof the protective housing and the anode waste gas stream can beintroduced freely into the circulating cathode gas stream. Whereas a gasdistributor and gas collector are provided in ordinary fuel cell stacksat each anode input, anode output, cathode input and cathode output,which must be sealed relative to the fuel cell stack in costly fashion,in the known system of the applicant, owing to the cathode gas streamfreely circulating in the protective housing, a gas distributor sealedrelative to the fuel cell stack is provided at the anode input, but nogas distributor is necessary at the cathode input so that the overalldesign can be significantly simplified.

The known fuel cell arranged by the applicant is described in detail,for example, in the international patent applications WO 96/02951 A1 andWO 96/20506 A1 and in German patent application DE 195 48 297 A1,incorporated herein in their entirety.

The essential components of the known fuel cell arrangement areschematically depicted in FIGS. 1 and 2 in a frontal and lateralcross-sectional view. The fuel cell arrangement designated overall withreference number 10 has a horizontally lying fuel cell stack 11, i.e.,consisting of vertically arranged, plate-like elements, which isarranged in a heat-insulated, gas-tight protective housing 12. Fuel gasis supplied via a fuel gas line 13 into the interior of the gas-tightprotective housing 12 and introduced into the anode chambers of the fuelcell stack 11 in a fuel gas distributor 16 arranged on the anode input15 on the bottom of the fuel cell stack 11 via a heat exchanger 14. Thefuel gas flows through the anode chambers in essentially a verticaldirection and emerges again on the anode output side 17 situated on thetop of the fuel cell stack. The heat exchanger 14 is a gas/gas heatexchanger, which is traversed, on the one hand, by the fuel gas and, onthe other hand, by a stream of cathode gas circulated within thegas-tight protective housing 12.

The cathode gas enters the fuel cell stack 11 at the cathode input 18arranged laterally and leaves it at the cathode output 19 on theopposite side of the fuel cell stack. As can be deduced from FIG. 1, theflow directions of the cathode gas and fuel gas are perpendicular toeach other. Maintenance of the gas streams in the protective housing 12is accomplished by means of two fans 20, 21 arranged above the fuel cellstack 11, each of which are driven by electric motors 22, 23. A diffuser24 and a static mixer 25 following it are arranged directly above theanode output 17 of the fuel cell stack 11. The anode waste gas leavingthe anode output 17 is mixed with the cathode gas stream circulating inthe housing 12 in the static mixer 25. Fresh air is also introduced tostatic mixer 24 via a line 26. Under the action of fans 20, 21 the gasmixture of anode waste gas, circulated cathode gas and fresh air is fedinto a catalytic burner 27 arranged above the static mixer 25, in whichcombustible residual components of the anode waste gas are catalyticallyburned and converted to useful heat. The gas mixture leaving thecatalytic burner, which now contains the main components of the cathodereaction with oxygen and carbon dioxide, is directed via fans 20, 21 tothe cathode input 18, where it then flows through horizontally to thefuel cell stack 11. As mentioned above, after emergence at the cathodeoutput 19, a partial stream of the cathode gas is fed back to the staticmixer 24. A start heater 28 is preferably arranged in front of thecathode input 18, which brings the process gases to the operatingtemperature of about 600° C. during startup of the fuel cell arrangement10. A diffuser 29 can also be arranged in front of the cathode input 18,which is supposed to permit homogeneous flow against the cell stacktogether with additional internals provided between fans 20, 21 and thecathode input 18. However, if, as in the depicted example, the heatexchanger 14 is also arranged in front of the cathode input 18,homogeneous flow against the cell stack can also be guaranteed by anappropriate configuration of the heat exchanger so that the additionaldiffuser 29 can optionally be dispensed with. Excess cathode exhaustleaves the fuel cell stack 11 via a cathode exhaust line 30 shown onlyschematically here.

The fuel cell arrangement described here is marketed by the applicantunder the name HM 300 in a circular cylindrical protective housing.

In this known design principle the static mixer, the catalytic burnerand the fans connected to them are directly arranged above the anodeoutput of the fuel cell stack, which imposes high flow requirements onthe circulation fan, namely both with respect to suction behavior of thefan in order to guarantee uniform mixing of fresh air, anode waste gasand cathode exhaust in the static mixer, and with respect to outflowbehavior of the fan in order to guarantee uniform flow against the cellstack by the gas mixture. These requirements can be guaranteed in theprevious design only by rectifiers and internals in the flow path,which, however, lead to pressure losses, which again requires higher fanpower. In cell stacks with several hundred individual cells several fansarranged along the cell stack are also required in order to achievehomogeneous flow behavior.

A further drawback of the previous design is that the catalytic burneris arranged above the cell stack between the static mixer and fan. Thecatalyst during the operating time, however, is exposed to soiling,which can lead to a deterioration in flow and additional pressure lossesso that the catalyst must regularly be cleaned. In the previousarrangement, however, the complete cell stack must be disassembled forthis purpose, which is connected with a very high work cost and can onlybe conducted by the manufacturer.

Another drawback of the known design is that the mixer must be designedvery compact directly above the anode output because of the limitedspace available so that satisfactory mixing can only be achieved bynumerous internals with correspondingly high pressure loss. Themanufacturing costs of the previously used mixer are therefore high.

Finally, the previous fuel cell arrangement permits only a few designdegrees of freedom. The ratio of height and width of the fuel cell stackand the additional components arranged in the protective housing isessentially stipulated by the use of a circular cylinder protectivehousing and the degrees of freedom with respect to arrangement anddimensioning of the components arranged in the protective housing arelimited. The layout of individual components specifically adapted toeach other also means that numerous components must be newly designed,depending on the power layout of the system. The assembly cost of thepreviously used fuel cell arrangement is also high.

The underlying technical problem of the present disclosure is thereforeto further improve the described design principle of a fuel cell stackintegrated in a protective housing with cathode gas stream circulatingin the protective housing.

In one embodiment of the present disclosure solves these technicalproblems by providing a fuel cell arrangement with at least onehorizontally arranged fuel cell stack, which has numerous fuel cells,each of which includes an anode, a cathode and an electrolyte arrangedbetween the anode and cathode. At least one fuel gas feed device appearsto feed fuel gas to the anodes of the fuel cells. An anode gaswithdrawal device to withdraw the anode waste gas from the anodes, and acathode gas feed device to feed cathode gas to the cathodes of the fuelcells. A cathode gas withdrawal device is present to withdraw cathodeexhaust from the fuel cells and at least one return device to return atleast part of the anode waste gas and/or cathode exhaust to the cathodesof the fuel cells. The return device has at least one catalytic burnerwith catalyst material for burning of residual combustible gas containedin the anode waste gas, which is arranged laterally next to the fuelcell stack.

It is proposed according to the one embodiment of the disclosure not todraw off the mixture of fresh air, anode waste gas and cathode exhaustafter passing through the catalytic burner directly by the fan, but tocollect it initially in a suction tube, which discharges into the fan.Mixing and catalytic burning of the drawn-in gas already occurs beforethe suction tube so that optimal suction by the fan is guaranteed.Because of flow guiding in a suction tube the fan can be arranged nextto the protective housing and communicate with the internal space of thehousing through standardized suction and discharge connectors. Since theprotective housing and the flanged-on fan form two separate assemblies,both assemblies can be designed and optimized independently of eachother. An optimized distributor for longitudinal distribution of the gasmixture coming from the fan can be arranged in the space gained abovethe cell stack so that the suction and outflow properties of the fanitself are not critical. Uniform flow against the cell stack isguaranteed without demanding rectifiers and internals by means of a flowdistributor that tapers wedge-like in the longitudinal direction of thefuel cell stack so that pressure losses can be significantly reducedrelative to the previous design. The power requirements on the fan arealso reduced accordingly. It was surprisingly found that cell stackswith up to 600 individual units can be supplied with a single fan withthe arrangement proposed according to the disclosure.

It is also proposed according to the disclosure to arrange the catalyticburner on the cathode output side between the fuel cell stack and thewall of the protective housing. Because of this arrangement the catalystis more readily accessible so that maintenance for cleaning purposes issimplified. For example, cleaning/filling openings can be provided inthe wall of the protective housing so that disassembly of the cell stackis no longer required. Cleaning of the catalyst can therefore be carriedout by the user. In contrast to the previously used fuel cellarrangement the catalytic burner is traversed from the top down so thatthe use of pelletized catalysts is now also made possible. In the priorart pelletized catalysts could not be used, since suspension of thecatalyst particles in the air stream occurs during flow from the bottomup, which entails strong mechanical wear on the catalyst elements.However, the previously preferably used honeycomb catalysts can likewisealso be used in the present disclosure.

A simple gas mixer with lower pressure losses is also furnishedaccording to the disclosure. The gas mixer has a first mixing zone inwhich cathode exhaust is mixed with fresh air, as well as a secondmixing zone in which anode waste gas is introduced to the mixture ofcathode exhaust and fresh air. The mixer is preferably arranged on thecathode output side between the cell stack and the wall of theprotective housing above the catalytic burner also provided there. Longmixing zones can therefore be implemented so that fewer internals andmixing elements are required in order to guarantee homogeneous mixing ofthe cathode and anode waste gas streams and the fresh air. The pressureloss in the mixture relative to the known mixers arranged on the fuelcell stack is therefore significantly reduced. In addition, the mixeraccording to the disclosure can be made light and can be easily and costeffectively manufactured because of the simple sheet metal parts, whichreduces the overall cost of the fuel cell arrangement.

The fuel cell arrangement according to the one embodiment of thedisclosure is arranged in functional groups that can be dimensioned andoptimized largely independently of each other.

One functional group then consists of a fuel cell stack with anode inputgas distributor and the anode output gas collector. In contrast to theordinary design in which the fuel cell stack also included componentslike the heat exchanger, static mixer and catalytic burner, the nowproposed assembly can be constructed much more simply. Anotherfunctional group consists of the cathode gas feed with distributorchannel, start heater and heat exchanger. This functional group can bepreassembled completely outside the container and integrated beforeinsertion of the stack.

Another functional group consists of the mixer and catalyst unit withsheet metal internals for mixing of fresh air, cathode exhaust and anodeoutput gas, the catalyst housing and catalyst output flow collector withbaffles.

Another functional group consists of the circulating fan with impellerhousing and connections on the suction side via a suction tube to thecatalyst output housing and on the pressure side to the cathode gasdistributor channel.

It is proposed according to the disclosure to design the protectivehousing rectangular so that the design of the components of the fuelcell arrangement according to the disclosure is independent of the widthto height ratio.

The functional group can be largely preassembled outside the module,which facilitates and accelerates assembly.

The disclosure is further explained below with reference to a practicalexample depicted in the accompanying drawings.

In the drawings

FIG. 1 shows a frontal cross-sectional view of a fuel cell arrangementof the prior art;

FIG. 2 shows a lateral cross-sectional view of a fuel cell arrangementof the prior art;

FIG. 3 shows a frontal cross-sectional view of a fuel cell arrangementaccording to one variant of the disclosure;

FIG. 4 shows an enlarged detail view with an area of FIG. 3 marked withcircle IV;

FIG. 5 shows a lateral cross-sectional view of the fuel cell arrangementaccording to the disclosure depicted in FIG. 2 along line V-V in FIG. 3;

FIG. 6 shows a top cross section of the fuel cell arrangement accordingto the disclosure depicted in FIG. 2 along line VI-VI of FIG. 3; and

FIG. 7 shows a schematic perspective view of the gas-tight housing of avariant of the fuel cell arrangement of FIGS. 3-6.

The fuel cell according to the prior art was already described above inconjunction with FIGS. 1 and 2.

With reference to FIGS. 3 to 7 two preferred variants of the fuel cellarrangement according to the disclosure are described below. Componentsthat are identical to components of the fuel cell arrangement of theprior art or have the same or similar function are then referred to withthe same reference numbers.

The fuel cell arrangement designed overall with reference number 10,like the fuel cell arrangement of the prior art, has a horizontallylying fuel cell stack 11 consisting of vertically arranged plate-likeelements, which is arranged in a heat-insulated, gas-tight protectivehousing 12. In contrast to the protective housing of the fuel cellarrangement of the prior art, the protective housing of the fuelarrangement 10 according to the disclosure is designed essentiallyrectangular. The gas-tight protective housing 12 consists of individualmetal plates 31 connected to each other, for example, welded to eachother, which, as is especially recognizable in FIG. 7, are stabilized onthe outside by steel supports 32, which impart the necessary rigidity tothe overall fuel cell arrangement 10. An appropriate insulation material29 for heat insulation of the internal space of the protective housing12 is applied to the inside of metal plates 31. The protective housing12 can be easily adapted to the altered dimensions of the fuel cellstack, which thus permits cost-effective production of fuel cellarrangements with different power.

The fuel cell stack 11 again has a cathode input side 18, cathode outputside 19, an anode input side 15 and an anode output side 17.

Fuel gas arrives in the interior of the gas-tight protective housing 12via fuel gas feed devices, which include a fuel gas line 13, and isinitially passed through a heat exchanger 14, which, in contrast to theprior art, is arranged above the fuel cell stack 11. The heat exchanger14 is also designed as a gas/gas heat exchanger in the fuel cellarrangement 10 according to the disclosure, which is traversed on oneside by the fuel gas and on the other side by a stream of cathode gascirculating within the gas-tight protective housing 12 so that the fuelgas is preheated before introduction into the fuel cell stack 11. Afterpassing through heat exchanger 14, the heated fuel gas reaches a fuelgas distributor 16 arranged on the bottom of the fuel cell stack 11 viaa line 33 arranged on the end of the fuel cell stack, which distributesthe fuel gas to the anode chamber inputs of the individual fuel cells ofthe stack. In the depicted example the fuel gas, however, does notdirectly enter the anode chambers. Instead reformer elements designedplate-like are arranged between the cell elements of the fuel cell stack11, which reform at least part of the fuel gas before introduction intothe anode chambers of the fuel cells in known fashion. The heated anodegas in the special variants of the disclosure depicted in FIGS. 3 to 6is supplied via line 33 initially into an edge strip formed as a hollowline 34 of the anode gas distributor 16, which serves as longitudinaldistributor. Along the hollow line 34 numerous distributor lines 35branch off laterally, which supply the fuel gas into the inputs of theseparate plate-like reformer units of the fuel cell stack via V-shapeddistributor heads 36 arranged on the ends of the distributor lines.After passing through the reformer units, which can be arranged, forexample, alternating with fuel cell elements in the fuel cell stack 11,or which are provided after a certain number of fuel cell elements, forexample, always after five fuel cell elements, the at least partiallyreformed fuel gas is returned into the interior of the fuel gasdistributor 16 and goes from there to the anode inputs of the fuel cellelements of the stack. In a preferred variant of the fuel cellarrangement according to the disclosure, in addition to these separatereformer elements for the so-called indirect internal reforming,reformer catalyst for the so-called direct internal reforming isarranged in the anode chambers of the fuel cell elements. Sealingbetween the distributor lines 35 and the internal space of the fuel gasdistributor 16 is therefore not critical because unreformed fuel gasthat directly reaches the internal space of the fuel gas distributor 16through possible leaks can also be directly reformed in the fuel cellelements. After flowing through the fuel cell stack 11 from the bottomup, the anode waste gas emerges at the anode output 17 on the top of thefuel cell stack 11 and is trapped by an anode waste gas collector 37 andfed laterally to a gas mixer 25, which is apparent in FIG. 3 andespecially in the enlarged depiction in FIG. 4 and is described indetail further below.

The cathode gas circulating in the gas-tight protective housing 12enters the cathode chambers of the fuel cell elements on the opencathode input side 18 of the fuel cell stack 11 and leaves the stack onthe cathode output side 19 after passing through the fuel cell stackessentially horizontally, on which a cathode exhaust collector 38 isarranged. The cathode exhaust collector 38 is connected via openings 39to a cathode exhaust line 40, via which excess cathode exhaust is takenoff from the fuel cell arrangement 10. Part of the cathode exhaust,however, also circulates in the protective housing 12 and, after mixingwith the anode waste gas and the fresh air in the gas mixer 25 andsubsequent after-burning in a catalytic burner 27 described furtherbelow, enters the fuel cell stack 11 again on the cathode input side 18as so-called cathode gas.

The cathode exhaust collector 38 arranged on the cathode output side hasa gap opening 42 extending essentially over the entire length of thefuel cell stack 11 in its upper area 41, through which the circulatingfraction of the cathode exhaust in the protective housing 12 reaches thedownstream gas mixer 25. The gas mixer 25 has a first mixing zone 43, inwhich the cathode exhaust leaving the cathode exhaust collector via thegap opening 42 and fresh air are introduced. The fresh air is fed via afresh air line 26 running essentially parallel to the fuel cell stack,which has at least one opening 44 along the mixer, for example, a gapopening running in the longitudinal direction, or several openings,through which fresh air can enter the first mixing zone 43. The gasmixer 25 also has a second mixing zone 45 arranged downstream over thefirst mixing zone 43, into which anode waste gas is introduced to themixture of cathode exhaust and fresh air. The gas stream runsessentially horizontally in the first mixing zone 43, whereas it isdeflected downward in the transitional region 46 from the first tosecond mixing zone. The gas mixer 25 is also designed so that the flowcross section of the first mixing zone 43 and the flow cross section ofthe inflowing anode waste gas is tapered to the second mixing zone 45 sothat the anode waste gas and the already premixed mixture of cathodeexhaust fresh air are accelerated to the second mixing zone 45. At thelevel of the first mixing zone and in the transitional region from thefirst to second mixing zones the anode gas stream and the stream of themixture of cathode exhaust and fresh air run essentially parallel sothat the anode waste gas stream is introduced essentially tangentiallyinto the mixture of cathode exhaust and fresh air. In the region of thefirst mixing zone 43 the anode waste gas stream and the mixture ofcathode exhaust and fresh air are separated by a baffle 47, which endsin the transitional region from the first to second mixing zones. Thisend of the baffle 47 has a number of tongues 49, which are bent upwardor downward in alternation in the longitudinal direction and are weldedto the top 50 or bottom 51 of the housing 52 of the gas mixer 25. Thesetongues 49 ensure additional swirling of the gas mixture and guaranteehomogeneous mixing of the anode waste gas, cathode exhaust and freshair. In addition or as an alternative, other static mixing elements canbe provided. The second mixing zone 45 also includes a distributor 53,which widens from a first flow cross section at the input 54 of thedistributor to a second flow cross section at the output 55 of thedistributor, in which the flow cross section at the output of thedistributor essentially corresponds to the surface of the inlet openingon the top of a catalytic burner 27 arranged after the gas mixer 25 forburning of the fuel gas contained in the anode waste gas. As isespecially apparent from FIG. 3, the gas mixer 25 is arrangedessentially between the fuel cell stack and a side wall 56 of thegas-tight protective housing enclosing the fuel cell stack. Relative tothe prior art, longer mixing zones can therefore be implemented. Moreeffective mixing can also be achieved without excessive use of numerousstatic mixing elements that increase flow resistance.

The catalytic burner 27 following the gas mixer 25 is also arrangedlaterally next to the fuel cell stack 11 on the side wall 56 of thegas-tight protective housing 12. The catalytic burner 27 has a top withat least one inlet opening 57, which communicates with the gas mixer 25for mixing of anode waste gas, cathode exhaust and fresh air. Thecatalytic burner has at least one outlet opening 58 on its bottom, whichcommunicates with a collector 59 for collection of the waste gases to bereturned to the cathode input. The catalytic burner 27 can include, forexample, a honeycomb catalyst. Due to flow guiding of the waste gasproposed according to the disclosure from the top down through thecatalyst, the catalyst material is not exposed to increased abrasion sothat the catalytic burner 27 according to the disclosure can bedesigned, in particular, as a pelletized catalyst. Owing to lateralarrangement next to the fuel cell stack, the catalytic burner 27 issituated in the immediate vicinity of a side wall 56 of the protectivehousing 12 of the fuel cell arrangement 10 according to the disclosureso that the catalyst material can be cleaned or replaced particularlysimply. For this purpose, one or more cleaning openings are provided inthe side wall 56 of the protective housing 12 of one or more cleaningopenings 60. The cleaning openings 60 are recognizable, in particular,in the perspective view in FIG. 7 of a variant in the version of FIGS. 3to 6. Catalyst material can be drawn off through the cleaning openings60 by means of a suction fan, for example. In contrast to the prior art,no demanding disassembly is therefore required. Access can be achieveddirectly to the catalyst material via the cleaning openings 60 and theside wall 56, for example if the catalytic burner has a permanentlyopened access at a corresponding height and largely gas-tight sealing ofthe edge of the access is guaranteed with the inside of the side wall 56of the protective housing 12. As in the depicted variant, the catalyticburner 27 or the oblique section of the distributor 53 lying directlyabove it has a closable access opening 61 to the catalyst material atthe level of cleaning opening 60 (cf. FIG. 5).

To maintain circulation of the cathode gas, i.e., the mixture of cathodeexhaust, anode waste gas and fresh air finely burned in the catalyticburner, return devices to return at least part of the anode waste gasand at least part of the cathode exhaust to the cathode inputs 18 andthe cathode chambers of the fuel cells of stack 11 are provided. Thereturn devices include at least one collection line 59 arranged on alongitudinal side of the fuel cell stack for collection of the returnwaste gases, which discharges into an inlet 62 of a feed device arrangedon the front of the fuel cell stack, which includes circulation fan 20and an electric motor 22. The circulation fan has an outlet 63, whichcommunicates with the cathode gas feed devices, which supply the gasmixture to the input of the cathode chamber.

Collection line 59 is an essentially horizontally running collectionline that extends over essentially the entire length of the fuel cellstack 11 in the foot area of the fuel cell stack 11. Numerous baffles 64are arranged in the collection line 59, which deflect the vertical gasstream coming from the gas mixer 25 and catalytic burner 27 into ahorizontal gas stream along the longitudinal axis of collection line 59.The baffles 64 are designed as bent sheets and are arranged offsetrelative to each other in the horizontal and vertical direction so thatuniform horizontal flow without additional swirling is generated. Thebaffles are preferably arranged on a space diagonal that runs from thelower end of the horizontal section of the collection line 59 away fromthe inlet 62 of the circulation fan 20 to the upper end of thehorizontal section of collection line 59 directed toward the inlet 62.Baffles 65 are again arranged on the end of the horizontal section ofcollection line 59, which divert the gas stream upward into anessentially vertical line section 66 to the inlet 62 of circulation fan20. At the outlet 63 of the circulation fan 20 the gas distributor 67 isconnected, which extends essentially over the entire length of the fuelcell stack in the head area of the fuel cell stack. The gas distributor67 has lateral outlet opening 68 arranged parallel to its longitudinalaxis, through the gas mixture can flow into a heating device 28 servingas start heater arranged after the outlet openings of the gasdistributor. As is apparent especially in FIG. 6, the cross-sectionalsurface oriented perpendicular to the longitudinal axis of the internalspace of gas distributor 67 tapers from its end arranged at the outlet63 of the circulation fan 20 to its opposite end so that the amount ofgas emerging laterally from the outlet opening 68 is essentiallyconstant over the entire length of the gas distributor 67. The startheater 28 arranged after the gas distributor 67 during startup of thefuel cell arrangement 10 heats the circulating gas mixture to theoperating temperature. The already mentioned heat exchanger 14 isconnected directly to the start heater 28, in which the circulatingcathode gas is brought into thermal contact with the fuel gas introducedto the protective housing 12. After flowing through the heat exchanger14, the circulating cathode gas flows freely through the internal space69 of the protective housing 12 back to the input 18 of the fuel cellstack 11 on the cathode side.

The variant of the fuel cell arrangement according to the disclosuredepicted in FIG. 7 differs from the variant depicted in FIGS. 3 to 6only in that in the variant according to FIG. 7 the fuel cell line 13discharges linearly at the level of the heat exchanger 14 into theprotective housing 12, whereas the fuel cell line 13 in the variant ofFIGS. 4-6 discharges into the protective housing beneath the fresh airline 26 and, as is especially apparent in FIG. 5, is deflected upward inthe direction of the heat exchanger 14 within the protective housing.

As can be deduced in the variants depicted in the figures, the fuel cellarrangement according to the disclosure favors a modular design fromlargely independent assemblies that communicate with each other viastandardized interfaces.

In a fuel cell arrangement according to the disclosure a first assemblyincludes the fuel cell stack 11 with the fuel gas feed devices,especially the fuel gas line 13 and the fresh air feed line, and theanode gas withdrawal devices, especially the anode waste gas collector37. The anode gas collector 37 is tightened by means of a clampingdevice 70 in the housing with the fuel cell stack and the fuel gasdistributor 16 arranged at the anode input.

The second assembly includes the cathode gas feed device with cathodegas distributor 67, start heater 28 and heat exchanger 14, which aremounted in an assembly frame 71 on the bottom of the cover 72 of theprotective housing 12.

The third assembly includes the cathode exhaust collector 38, a cathodeexhaust line 40, a gas mixer 25 for mixing of fresh air, cathode exhaustand anode waste gases, a catalytic burner 27 and a collection line 59 ofthe return device. In the depicted variant the third assembly is dividedinto a first subassembly, which includes the cathode exhaust collector38 and the cathode exhaust line 40, as well as a second subassembly,which includes the gas mixer 25, the catalytic burner 27 and thecollection line 59 of the return device.

Finally a fourth assembly includes the feed device of the return device,which consists of a circulation fan 20 with an impeller housing 72 andconnections 63 on the suction side, which communicate with thecollection line 59 of the third assembly, and connections 64 on thepressure side, which communicate with the cathode gas distributor 67 ofthe second assembly, as well as the electric motor 22 to drive thecirculation fan 20.

The assemblies are arranged in the interior of the gas-tight protectivehousing 12, in which the protective housing has an essentially cuboidgeneral shape.

A particular advantage of the arrangement according to the oneembodiment of the disclosure is seen in the fact that the second andfourth assemblies can be connected beforehand to the inside walls of theprotective housing before the first and third assemblies are inserted.

Those skilled in the art recognize the words used are words ofdescription, and not words of limitation. Many variations andembodiments will be apparent without departing from the scope and spiritof the invention as set forth in the appended claims.

1. A fuel cell arrangement with at least one horizontally arranged fuel cell stack, which has numerous fuel cells, each of which includes an anode, a cathode and an electrolyte arranged between the anode and cathode; at least one fuel gas feed device to feed fuel gas to the anodes of the fuel cells; at least one anode gas withdrawal device to withdraw the anode waste gas from the anodes, at least one cathode gas feed device to feed cathode gas to the cathodes of the fuel cells, at least one cathode gas withdrawal device to withdraw cathode exhaust from the fuel cells and at least one return device to return at least part of the anode waste gas and/or cathode exhaust to the cathodes of the fuel cells, characterized by the fact that at least one return device having at least one catalytic burner with catalyst material for burning of residual combustible gas contained in the anode waste gas, which is arranged laterally next to the fuel cell stack.
 2. The fuel cell arrangement according to claim 1, characterized by the fact that the catalytic burner has a top with at least one inlet opening, which communicates with a gas mixer for mixing of anode waste gas, cathode exhaust and/or fresh air.
 3. The fuel cell arrangement according to one of the claim 1, characterized by the fact that the catalytic burner has a bottom with at least one outlet opening, which communicates with a collection line for collection of the waste gases being returned.
 4. The fuel cell arrangement according to one of the claim 1, characterized by the fact that the catalytic burner includes a honeycomb catalyst.
 5. The fuel cell arrangement according to one of the claim 1, characterized by the fact that the catalytic burner includes a pelletized catalyst.
 6. The fuel cell arrangement according to one of the claim 4, characterized by the fact that the catalytic burner is accessible from the outside via at least one cleaning opening, via which the catalyst can be replaced.
 7. The fuel cell arrangement according to claim 6, characterized by the fact that the fuel cell arrangement is enclosed by a gas-tight protective housing and that the catalytic burner is arranged on the inside of a side wall of the protective housing, the cleaning opening being designed as a closable cleaning opening in the side wall of the protective housing.
 8. The fuel cell arrangement according to claim 7, characterized by the fact that the catalytic burner is arranged between the cathode output side of the fuel cell stack and the side wall of the protective housing containing the at least one cleaning opening. 